Gram-positive and gram-negative bacteria may cause life-threatening disease in infected patients. There is an increased incidence of such infections in prematurely born infants and patients who have serious underlying medical conditions. Newborns have an immature immune system and are acutely susceptible to sepsis and meningitis caused by certain species of gram-negative and gram-positive bacteria. Encapsulated strains of Escherichia coli. Neisseria meningitidis group B, Hemopohilus influenzae type B, and Streptococcus agalactiae (group B streptococcus) comprise the majority of isolates in neonates, although other isolates may also cause such infections. Regardless of whether the infant develops the infection at birth (early onset) or within the first weeks of life (late onset), mortality and morbidity rates remain high, despite aggressive medical intervention.
The group B streptococcus is the predominant gram-positive bacterium causing severe or life-threatening neonatal infections (Baker, 1986, N. Engl. J. Med. 314:1702). The group B streptococci are identified by a group-specific carbohydrate, the B polysaccharide, and may be further divided into five serotypes, Ia, Ib, Ic, II, and III based on serologically diverse capsules. Strains from the capsule types Ia, Ib, II and III are the predominant clinical isolates, any of which may cause neonatal sepsis; type III capsular strains are associated with the majority of cases of neonatal meningitis. Baker et al., 1976, N. Engl. J. Med. 294:753. Among gram-negative organisms causing meningitis in the neonatal population, the encapsulated E. coli strain K1 is the primary isolate.
Antibiotics have long been the primary therapeutic tool for the control and eradication of gram-positive and gram-negative infections. The continued incidence and severity of the infections, the continual emergence of antibiotic resistant bacterial strains, and the inherent toxicity of some antibiotics, however, illustrate the limitations of antibiotic therapy. These observations have prompted searches for other prophylactic and therapeutic approaches.
Antibodies may provide an alternative means for eliminating bacteria from an infected individual or for preventing their colonization in uninfected individuals at risk for developing disease. It is believed that antibodies which bind with antigens accessible (externally exposed) on live bacteria may facilitate bacterial destruction, which process may occur by any of several mechanisms, including (1) direct lysis of the bacteria in the presence of serum complement, (2) bacteriostasis, by the blockading of nutrient scavenger receptors, (3) opsonization and subsequent phagocytosis of the bacteria in the presence or absence of serum complement, or (4) prevention of attachment of the bacteria to host tissues (Mims, C. A., "Recovery from Infection," in The Pathogenesis of Infectious Disease. pp. 198-222, Mims, C. A., Ed., Academic Press (1982)). For bacteria that possess surface carbohydrate molecules, such as lipopolysaccharide (LPS) and/or capsules, antibody appears to be most effective via opsonization mechanisms (Kaijser, B., et al., "The Protective Effect Against E. coli of O and K Antibodies of Different Immunoglobulin Classes," Scand. J. Immunol. 1:276 (1972)). Therefore, antibodies directed to accessible carbohydrate structures may provide an effective regimen for therapy or prophylaxis.
In general, mammals that are exposed to disease-producing bacteria produce antibodies that are specific for LPS or capsule. These antigens, which often form the basis for serotyping the bacterial strains, are chemically diverse structures composed of frequently repeating oligosaccharide molecules. Since LPS or capsule are often the immunodominant bacterial antigens, serotype specific antibodies have been the most studied of potentially therapeutic antibodies. However, because of the strain specificity of these antibodies, and the diversity of carbohydrate antigens on pathogenic gram-positive and gram-negative bacteria, it would be extremely difficult and costly to produce a therapeutic formulation containing only serotype specific antibodies (see, e.g., Kaijser, B. and Ahlstedt, S., "Protective Capacity of Antibodies Against Escherichia coli O and K Antigens," Infect. Immun. 17:286-292 (1977); and Morrison, D. C. and Ryan, J. L., "Bacterial Endotoxins and Host Immune Response," Adv. Immunol. 28:293-450 (1979)). Regardless, various reports have stimulated visions that immunotherapeutic approaches could be found to treat bacterial disease.
Fractionated human plasma, enriched for immune globulins containing specific and protective antibodies against the infection organisms, have been somewhat effective against Pseudomonas aeruginosa infections. (Collins, M. S. and Robey, R. E., "Protective Activity of an Intravenous Immune Globulin (Human) Enriched in Antibody Against Lipopolysaccharide Antigens of Pseudomonas aeruginosa," Amer. J. Med. 3:168.174 (1984)). However, certain inherent limitations have prevented the widespread use of immune globulins in the treatment of life-threatening bacterial disease For instance, such compositions are assembled from large pools of plasma samples that have been preselected for the presence of a limited number of particular antibodies Typically, these pools consist of samples from a thousand donors who may have low titers to some pathogenic bacteria. Thus, at best, there is only a modest increase in the resultant titer of desired antibodies.
Another such limitation is that the preselection process itself requires very expensive, continuous screening of the donor population to assure product consistency. Despite considerable effort, product lots can still vary between batches and geographic regions.
Yet another such limitation inherent in immune globulin compositions is that their use results in coincident administration of large quantities of extraneous proteinaceous substances (e.g., viruses) having the potential to cause adverse biologic effects The combination of low titers of desired antibodies and high content of extraneous substances often limits, to suboptimal levels, the amount of specific and thus beneficial immune globulin(s) administrable to the patient.
In 1975, Kohler and Milstein reported that certain mouse cell lines could be fused with mouse spleen cells to create hybridomas which would secrete pure "monoclonal" antibodies (Kohler, G. and Milstein, C., "Continuous Cultures of Fused Cells Secreting Antibody of Predefined Specificity," Nature 256:495-497 (1975)). Using this technology, mouse monoclonal antibodies specific to certain capsule serotypes of group B streptococci have been reported to be protective in experimental animal models (see. e.g., Egan, M. L. et al., "Protection of Mice from Experimental Infection with Type III Group B Streptococcus Using Monoclonal Antibodies," 1983, J. Exp. Med., 1:1006-1011, Shigeoka et al., 1984, J. Inf. Dis. 149:363; and Yoder et al., 1986, Pediat. Clin. N. Amer. 33:481). These studies followed earlier work which had shown that heterologous antisera possessing group B streptococcus type-specific antibody was protective in animals (e.g. Lancefield, 1972, Streptococci and Streptococcal Disease (Wannamaker and Matson, Eds, Academic Press, NY, p.57), and Lancefield et al., 1975, J. Exp. Med. 142:165).
Retrospective clinical studies comparing healthy human neonates with those infected by group B streptococci have also shown that low infection rates correlated best with elevated maternal and type-specific antibody titers, while increased rates of infection occurred among premature infants with the lowest antibody titers. Christensen et al., 1984, Eur. J. Pediatr. 142:86 and Gotoff et al., 1986, J. Infect. Dis. 153:511. Moreover, passively administered human serum immunoglobulin preparations containing capsule type-specific antibodies conferred protection to animals against group B streptococci of the corresponding capsule type Lancefield et al. 1975, supra, and Gotoff et al. supra. High antibody titers against the group B carbohydrate did not apparently correlate with reduced infection rate (Anthony et al., 1985, J. Inf. Dis. 151:221) nor were murine monoclonal antibodies to the group B carbohydrate antigen protective in vivo (Shigeoka et al., supra).
Murine monoclonal antibodies have also been made which bind to and opsonize several K1-positive E. coli strains regardless of their LPS serotypes (Cross et al., 1983, J. Inf. Dis. 147:68, Soderstrom, T. et al., 1983, Prog. Allergy 33:259, and Cross, A. S., et al., "The Importance of the K1 Capsule in Invasive Infections Cause by Escherichia coli," J. Inf. Dis., 149:184-193 (1984)). Moreover, these monoclonal antibodies have been found to be protective in mice against lethal challenges with E. coli K1 and Group B meningococcal organisms (Cross, supra and Soderstrom, supra). The antibodies, of the IgM isotype, were derived from mice immunized with polysaccharide obtained from N. meningitidis group B.
A mouse monoclonal antibody, while useful in treating mice, has major disadvantages for use in humans The human immune system is capable of recognizing any mouse monoclonal antibody as a foreign protein. This can result in accelerated clearance of the antibody and thus abrogation of its pharmacological effect (Levy, R. and Miller, R. A., "Tumor Therapy with Monoclonal Antibodies," Fed. Proc. 42:2650-2656 (1983)). More seriously, this could conceivably lead to shock and even death from allergic reactions analogous to "serum sickness." Clinical experience has shown that anti-mouse immunoglobulin responses have limited the utility of these antibodies in approximately one-half of the patients receiving mouse monoclonal antibodies for treatment of various tumors (Sears, H. F., et al., "Phase I Clinical Trial of Monoclonal Antibody in Treatment of Gastrointestinal Tumor," Lancet 1:762-764 (1982); and Miller, R. A., et al., "Monoclonal Antibody Therapeutic Trials in Seven Patients with T-Cell Lymphoma" Blood. 62:988-995 (1983)).
Accordingly, there remains a significant and urgent need for human monoclonal antibodies which are protective against infections due to gram-negative and gram-positive bacterial pathogens important in neonatal sepsis and meningitis The present invention overcomes prior difficulties and fulfills the need for such compositions and methods of treatment, prophylaxis, and diagnosis.